Within the meaning of the present Application, liquid service fluids are understood to include, in particular, lubricating oil, engine oil, hydraulic oil and other such service fluids.
To optimize the service life of machines, it is increasingly vitally important to select the proper service fluids for the machines, such as, in particular, lubricating oil for combustion engines. Under certain circumstances, unsuitable oil can lead to immediate failure of the machine, while an especially high-grade lubricating oil can ensure an above average operational life. During a manual filling operation, when changing or replenishing oil, errors caused by the inadvertent selection of an inappropriate lubricating oil cannot be ruled out. This is becoming ever more critical, since, to an increasing degree, motor vehicle engines require lubricating oils that are tailored and adapted to the specific engine type, for example. If an inappropriate service fluid is poured in, and this is not detected in time, substantial adverse consequences, such as premature failure of the machine, may arise.
In addition, the quality of a service fluid is decisive for determining its replacement interval. Today's motor vehicles do, in fact, already come equipped with on-board computers which calculate or adjust the oil replacement intervals as a function of various operating parameters. However, it is not possible to automatically consider the quality of the lubricating oil that has been poured in.
Dyes for marking fuels are already known from the patent literature. Thus, U.S. Pat. No. 6,274,381 B1 discusses using two or more visible dyes, whose absorption maxima are at distinct wavelengths from each other, in a fuel. By introducing a sample of such a marked fuel into a suitable laboratory apparatus, it is possible to identify the indicator. To this end, U.S. Pat. No. 6,274,381 B1 discusses using a light source and determining the absorption characteristic of the indicators.
Another method is known from U.S. Pat. No. 5,928,954. This document describes using fluorescing dye in the liquid to be marked. The indicator is detected in a laboratory apparatus which includes a sample holder into which a small amount of the substance to be investigated is introduced. The sample is then irradiated by laser diodes, and the fluorescence produced by the fluorescing dye is measured.
Another fluorescing dye for fuels is known from U.S. Pat. No. 5,729,967.